Method for synthesizing large single crystals of quartz



Jan. 9, 1951 1. 1. FRIEDMAN ET AL 2,537,043

METHOD FOR SYNTHESIZING LARGE SINGLE CRYSTALS 0F QUARTZ Filed April 29, 1948 GRMS Si 0 DISSOLVED IN lOml 0F SOLUTION TEMPERATURE C 4 GE R 1 III I 22 1 52 226E" E 29 an M55 INVENTORS ISIDORE l. FRIEDMAN PAUL H. EGLI ATTORNEY Patented Jan. 9, 1951 METHOD FOR SYNTHESIZING LARGE SINGLE CRYSTALS OF QUARTZ Isidore I. Friedman, Chicago, 11]., and Paul H. Egli, Washington, D. 0.

Application April 29, 1948, Serial No. 24,024

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 O. G. 757) 3 Claims.

This invention relates to a method and apparatus for quartz crystallization from an alkaliwater-silica system and in particular to a method for increasing the yield of quartz from such a system.

The general object of the invention is to grow large single crystals of quartz by crystallization from an alkali-water solution of silica.

It is also an object of the invention to increase the yield of quartz from a supersaturated solution of silica over that obtainable by mere supercooling.

It is a further object of the invention to grow such crystals efiiciently and at a rate of growth which is compatible with the formation of crystals free of flaws.

It is a still further object of the invention to provide apparatus which is suitable for carrying the various steps of the crystallization process into efiect.

Other objects will be apparent to those skilled in the art from the following description and from the drawings hereto appended which are merely illustrative of apreferred embodiment of the applicants invention and are not limitative thereof and in which;

Figure l. is a graphic illustration of the solubility, in grams per ten ml. of solution, of silica in aqueous solutions containing ten per cent NagO introduced as NaOH and NazCOs, respectively, as a function of the temperature.

Figure 2 is a schematic arrangement of apparatus for carrying the applicants invention into efiect.

Referring to Figure 1, here is shown at I a curve indicating the grams of silica dissolved in ten m1. of a ten percent solution of soda introduced as sodium hydroxide through a temperature range of from 250 C. to 450 C. Curve l2 shows the solubility in grams per ten ml. of solution of silica in a percent solution of soda introduced as sodium carbonate, through the same temperature range. Curve l 2 approaches curve ill with increasing rapidity from and above the temperature of about 350 C. The difierence in the amount of silica dissolved in the two solutions 7 is almost constant and at a maximum from about 250 to about 350 C. It is this maximum difference temperature range of these two curves shown by dash lines l4 and [6 with which the applicants invention is concerned. Obviously, if in an equilibrated solution of silica in sodium hydroxide the latter compound can be converted to the carbonate, a relatively large amount of, the silica will be forced out of solution of Tuttle and Friedman, Serial No. 37,176,

filed July 6, 194-8. The concentration of the components at a temperature of 350 C. is, as indicated by curve I0; Percent by weight NazO 10 S110: 33 H2O 57 This concentration is well within the area of quartz crystallization as defined in the above cited copending application.

Referring further to the solubility curves of Figure 1, it is seen that at 350 C. a ten percent solution of NagO introduced as sodium hydroxide will dissolve 3.3 grams of silica per ten ml. of solution; that at this same temperature a ten percent solution of NazO introduced as the carbonate will dissolve .66 gram of silica per ten ml. of solution. Thus it is apparent that by converting the hydroxide solution to the carbonate the difference of these solubilities, viz., 2.64 grams of silica per 10 ml. of solution will be forced out of solution. This silica will crystallize out as quartz if the concentration of the solution is as above indicated. A further study of the solubility curve shows that if the sodium hydroxide solution of silica be cooled from 350 C. to about 250 C. approximately 0.4 gram of silica will crystallize out as quartz per ten ml. of solution. If the sodium hydroxide solution is converted to the carbonate solution and cooled to approximately 250 C. the total yield of quartz will be 2.92 grams per ten ml. of solution. The increased yield by conversion over crystallization directly from the hydroxide solution is thus readily apparent.

The applicants have found that the sodium hydroxide solution of silica may be readily converted to the carbonate solution by pumping or forcing carbon dioxide into the solution. This conversion takes place in accordance with the equations:

2NaOH+COz- NazCOa +H2O 1) and Na2SizO5+C02- NaaCOs +2Si02 2) Equation (2) shows the conversion of sodium bisilicate to the carbonate by reaction with caring or forcing more carbon dioxide into the solution than that required by equation (1) the sodium hydroxide is converted to sodium bic rbonate as expressed by the following equation:

NaOH+CO2 NaI-ICs '(3) and that by way of illustration that sodium carbonate on an equivalent basis 'wvill-dissolvemore silica than the bicarbonate as shown bytthe'following equation:

Equations -(4) and (El) are reversible. There- .Ioreby pumping CO2 into the solution the solvent reaction is reversedand the dissolved silica crystallizes out as uartz.

The conversion or" the dissolved -,material 'to a silica and the solvent solution tothe carbonate and preferably to the bicarbonate constitutesthe essence of the applicants invention. The crys- .tallizationofiguartz from solution accordingtothe applicants method comrises a series of related steps which are dependent upon each other and which are carried out under close control as to rate, temperature, pressure and concentration.

The invention further includes an arrangement of apparatus for performing the various steps of 3 the method. This arrangementwhich is illustrated diagrammaticallyin Figure 210i the drawings comprises a storage tanlrfcr-GOZ '26 Which is supported and contained in a refrigerator or heat exchanger 22. Tank 2% is connected ,by -heavy tubing 26-, to' boiler 2i" which isrcontained in and supported by muflie furnacezs. This furnace is provided with a-mufiie 35). "Boiler 23 is connected'byheavytubing =32, reservoir 3'4 and heavy-tubing Qu to-the first member iii off-apair of magneticallyoperated valves 59 andie. Tubing 38 is provided"withapressure reading gauge 5! and atmospheric vent'val-ve et. Magnetic :valves 4% and areconnected by heavy tubing 42. They are arranged so that a definite vol- .ume of gas is contained between them. They may beioperated either byihand or preferably by a clock mechanism (not shown) so that gas may be passed onat;a definite rate. ilvlagneticvalve 34 is connected-by-tubing i185 and check valve 4 5 to react1on: chamber d8 Q-WillCh .is supported and contained inizfurnace This'furnace may be heated electrically or-byany other means which will give ,a controlled, uniform heat distribution. Chamber -13;,contains silicate solution 52 which at the beginning of ;the operation is the sodium ,hydroxideesilica solution zdefined supra. Quartz fragments 53 may be placed inzthe bottomof chamber 1-48. to be dissolved inthe sodium hydroxide in preparation of the solution. But this is not necessarilyso-since the solution may be prepared by the additionof: silica :gel, finely ground quartz glass or a higher isilica content sodium silicate to the hydroxide. Chamber 33 is provided with ra rotatable shaftfid which is positioned on'the vertical axis of the chamber and extends upwardly through the cover thereon. Shaft .54 -is provided with radial arms 55 on the extremities ,of .which are mounted .seed crystals "53.. Shaft 5 \is .provided at tits supper [iii , into .the reaction chamber.

end with driving means 58 which is adapted to rotate the shaft periodically first in a clockwise and then in a counterclockwise direction.

The operation of the applicants method and apparatus is as ,follows: vA ten liter solution of sodium hydroxide is prepared by adding about one thousand and thirty grams of sodium hydroxide to ten liters of Water. To this solution is added about three hundred and thirty grams floflf sil-ica whieh may be derived from finely ground quartz glass, quartz fragments, silica gel or from the highensilica-content water glasses. In case pf deriving the silica from water glasses care must be exercised in order to keep the total soda *contentof the solution below about twenty percent .by weight. The solution is then placed in the reaction chamber 48 in furnace 50, shaft 54 with seedzcrystalssiifi supported thereon is placed in position-and cover 39 is then tightly sealed on the reaction chamber. Heat is then applied to the reaction chamber ;by -me a r;is of ;f u rnace to raise the temperature uniformlyto about 7 325 C. flihe so1uti0n.;is;;he1d ,atthis temperature for rfrom :ten t wenty-t u iih rs o ll w the lution to come to equilibrium and to redissolve any spontaneous-nuclei of crystallization which {may havepformed. Shaft is now rotated by ,troducedinto the solutionsas iiollows: .vent valve ,36 is 'opcnedtojallow' the system up to thevent valve to become filled with carbon-dioxide. Boiler {2-8 is nowiheated by iurnace 29-:toa temperature at which=the pressure on-the-carbon dioxide will be about nv-e hundred pounds per square inch higher than the pressure in reaction chamber {These -pressures are shown -;on gauges Al and-1? respectively. 'Up to this pointjn the process magnetic .valves so and Mi have been closed. Valve 30 is now opened, valve 44 remaininglclosed, .toebringithe pressure-on the CO2 gas between these two .valves up to that indi- .catedby gauge Al. Valvefiii is now closed and valve-4 3 isopenedto permitthegas between the two valves .to expand through heavy tubing (25 Since a definite volume of gasiscontained betweenthe ,two valves, upon itsexpansion againstthe lower pressure, a definite .ouantity ,of .the carbon vdioxide gas .will be forced into the reaction chamber. .Magnetic valves Ail andlili. may be operated manually, but they are preferably operated by electrical switchescontrolled by. clock-.w ork,.so that the gas mayibeied intothe reaction chamber ata olefinite rate. :Theiorcing inpf the carbondioxide is continued ,until ,the sodium ;hydro xlde .is convertedtothebicarbonate of soda and-the sodium silicate is '-converted ,to the bicarbonate of soda with the formation ;;of .free; silica, the excess of which crystallizes outas quartz. The operation is repeatedeusingrthe same seed crystals, until crystals of the desired size are grown.

While the applicants ,have described a par ticular arrangement of apparatus as the preferred embodiment oitheir invention they do not desire i-to ,be strictly .l imited thereto since. other means such asa-pumping mechanism forintroducing the carbon :diox-ide ,may "be used with equivalentefiect and without departing from the spirit and scope of thezinvention. Such modificationsare. intended qto ;be included as comm-S within the scope of the invention to the extent as defined by the herewith appended claims.

The invention herein described may be made and used by or for the Government of the United States of America for governmental purposes without the payment of any royalty thereon or therefor.

What is claimed:

1. The method of growing large single crystals of quartz on seed crystals rotatably mounted within the following defined solution, comprising preparing a solution of silica in an alkali metal hydroxide at a temperature within the range of 350 C. to 450 C., equilibrating the solu tion at a temperature Within this temperature range for a period of time, cooling the solution at a predetermined rate to a temperature about fifty to one hundred and fifty degrees C. below the temperature of equilibration, forcing carbon dioxide into the solution at a slow rate of flow and in sufilcient quantity to convert the alkali metal hydroxide and the alkali metal silicate to alkali metal bicarbonates and free silica which precipitates out of said solution as quartz on said seed crystals and repeating these method steps using the same seed crystals until crystals of the desired size are grown.

2. The method of growing large single crystals of quartz on rotatably mounted seed crystals of quartz, comprising preparing an aqueous solution of ten percent by weight of soda introduced as sodium hydroxide in suflicient volume to cover said seed crystals, dissolving in this solution from about twenty nine to about thirty five percent by weight of silica derived from one of the following sources consisting of fragmental quartz, finely'ground quartz glass, silica gel and a sodium silicate higher in silica content than sodium bisilicate, heating the solution to a temperature Within the range of from about 250 C. to about 450 C. equilibrating the solution at the solution temperature for a period of time of from ten to twenty four hours, cooling the equilibrated solution at a rate of about two degrees per hour to a temperature of from fifty to about one hundred and fifty degrees below the temperature of equilibration, forcing carbon dioxide at a relatively slow rate of flow into the said solution to convert the sodium hydroxide and the sodium silicate, formed by the reaction of the silica with the sodium hydroxide, to the bicarbonate of soda and free silica, the excess of which over that soluble in the bicarbonate at the temperature of conversion precipitates out of solution as crystalline quartz on said seed crystals and repeating the method using the same seed crystals until crystals of the desired size are grown.

3. The method of growing large single crystals of quartz on rotatably mounted seed crystals of quartz, comprising preparing an aqueous solution of ten percent by weight of soda introduced as sodium hydroxide in suificient volume to cover said seed crystals, dissolving in this solution from about twenty nine to about thirty five percent by weight of silica from one of the following sources consisting of fragmental quartz, finely ground quartz glass, silica gel and a sodium silicate higher in silica content than sodium bisilicate, heating the solution to approximately 350 C., equilibrating the solution at this temperature for a period of time of from ten to twenty four hours, cooling the equilibrated solution at a rate of about two degrees per hour to a temperature of about 325 C., forcing carbon dioxide at a relatively slow rate of flow and in sufficient quantity to convert the sodium hydroxide and the sodium silicate, formed by the reaction of the silica with the sodium hydroxide, to the bicarbonate of soda and free silica, the excess of which over that soluble in the bicarbonate at the temperature of 325 C. precipitates out of solution as quartz on said seed crystals, cooling the bicarbonate solution to a temperature of about 250 C. to produce a further precipitation of quartz and repeating the method using the same seed crystals until crystals of the desired size are grown.

ISIDORE I. FRIEDMAN. PAUL H. EGLI.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 61,931 Fleury Feb. 12 1867 1,409,607 Stevens Mar. 14, 1922 1,430,900 Haferkamp Oct. 3, 1922 1,843,576 McClure Feb. 2, 1932 2,386,337 Moyer Oct. 9, 1945 2,424,273 Haas July 22, 1947 

1. THE METHOD OF GROWING LARGE SINGLE CRYSTALS OF QUARTZ ON SEED CRYSTALS ROTATABLY MOUNTED WITHIN THE FOLLOWING DEFINED SOLUTION, COMPRISING PREPARING A SOLUTION OF SILICA IN AN ALKALI METAL HYDROXIDE AT A TEMPERATURE WITHIN THE RANGE OF 350* C. TO 450* C. EQUILIBRATING THE SOLUTION AT A TEMPERTURE WITHIN THIS TEMPERATURE RANGE FOR A PERIOD OF TIME, COOLING THE SOLUTION AT A PREDETERMINED RATE TO A TEMPERATURE ABOUT FIFTY TO ONE HUNDRED AND FIFTY DEGREES C. BELOW THE TEMPERTURE OF EQUILIBRATION, FORCING CARBON DIOXIDE INTO THE SOLUTION AT A SLOW RATE OF FLOW AND IN SUFFICIENT QUANTITY TO CONVERT THE ALKALI METAL HYDROXIDE AND THE ALKALI METAL SILICATE TO ALKALI METAL BICARBONATES AND FREE SILICA WHICH PRECIPITATES OUT OF SAID SOLUTION AS QUARTZ ON SAID SEED CRYSTALS AND REPEATING THESE METHOD STEPS USING THE SAME SEED CRYSTALS UNTIL CRYSTALS OF THE DESIRED SIZE ARE GROWN. 